Hollow structure plate, manufacturing method thereof, manufacturing device thereof, and sound absorbing structure plate

ABSTRACT

Introduction guides  12  are provided above and below a sheet-introduction opening portion of a pressure-reduced chamber  10 , and heating means  17  is provided between the introduction guides. Each resin sheet  3  is attracted and attached respectively to the circumferential surface of a corresponding emboss roller  11  by reducing pressure. Pins  112  of the emboss roller  11  are truncated cone-shaped. The ratio of the total area of the lower bases of the pins  112  to the area of the circumferential surface of the emboss roller is 0.5 or more. The rising angle θ of the pin side face, in the vertical plane including the central axis of the pins  112 , is in the range from 50 degrees to 70 degrees. Furthermore, a multilayered hollow structure plate  140  is formed by attaching non-air-permeable sheets  130  onto both the front and back of a core member obtained by fusing together hollow protrusions  112  in two thermoplastic resin sheets. A sound absorbing material  150  is provided on at least one of the front and back side thereof, and small holes  114   a  opened in the multilayered hollow structure plate are formed in liner portions  114  and the non-air permeable sheet  130  only in the positions that matches the liner portions  114.

TECHNICAL FIELD

The present invention relates to hollow structure plates, methods andapparatuses for manufacturing the same, and sound absorbing structureplates.

BACKGROUND ART

Plastic hollow structure plates, such as flute-shaped plastic cardboards(product name: Danplate manufactured by Ube-Nitto Kasei Co., Ltd.),corrugated plastic cardboards, plastic structure plates in whichcolumnar independent air compartments are formed (product name: Plapearlmanufactured by Kawakami Sangyo Co., Ltd.), are lightweight and haveexcellent water resistance, heat resistance, chemical resistance andother properties, and thus have conventionally been used in variousapplications such as building panels, containers, various boxes, andinterior materials for, for example, houses, buildings, offices, andvehicles (e.g., see JP 2000-326430A as a honeycomb structure plate).

Among these, hollow structure plates in which columnar independent aircompartments (hereinafter, referred to as “hollow protrusions”) areformed are known to have no difference in strength between the verticaland the horizontal directions, compared with corrugated plasticcardboards or flute-shaped plastic cardboards.

Such a structure plate can be obtained by molding a thermoplastic resinsheet under a reduced pressure. In this structure, when it is attemptedto increase the height of a hollow protrusion to increase the thickness,the wall portion constituting the hollow protrusion turns into a film,so that the strength cannot be maintained. If the thickness of the resinsheet is increased in order to solve this problem, then the weight isinevitably increased and the property of being lightweight is impaired.Therefore, a technique disclosed in JP 2000-326430A has been developedas a conventional art of the present invention.

In this technique, a plurality of hollow protrusions are projected ineach of a pair of resin sheets, and the resin sheets are fused with thehollow protrusions facing each other, so that a hollow structure plateis obtained. By attaching the two sheets, the thickness can be madetwice as large as the conventional thickness while the strength ismaintained. Subsequently after the formation of the hollow protrusionsand the attachment process, a smoothly planed board or the like islaminated on the opposite surfaces of the two resin sheets, and thus aplate material product having a lightweight hollow structure can beobtained.

A method for manufacturing this structure, which is disclosed in theabove-mentioned publication, is as follows. Two resin sheets extrudedfrom a T-die are supplied between a pair of emboss rollers in which amultitude of pins are projected from their outer circumferentialportions, and the pressure inside the rollers is reduced and evacuated,so that the two resin sheets are molded so as to be pin-shaped under areduced pressure. At the same time, the pins are brought in contact witheach other with the rotation of the rollers so that the end faces of thehollow protrusions are thermally fused to become integral. In thisstate, the sheets are taken up by a take-up roller, and thus an integralhollow structure plate can be obtained.

However, the above-described manufacturing method has the followingtechnical problems in terms of the shape or the properties, and cannotbe adapted for manufacturing in practice.

First, often, the sheet cannot be attached onto the roller simply byevacuating the roller, and evacuation loss occurs, so that when forminghollow protrusions having a large height, molding is impossible.

Second, when the rollers are heated to a temperature at which the hollowprotrusions of the resin sheets can be molded, the resin sheets getattached to the rollers, which makes mold release difficult. Even ifmold-release is performed successfully, the shape is transformed becausethe temperature of the hollow protrusions is at least a melting point ormore. On the other hand, if the molding temperature is too low, then thebottom surfaces of the hollow protrusions cannot be fused and joinedtogether, even if they are in contact with each other. In such a case,the resin sheets are detached from each other at the joined portion whena bending load is applied to the obtained hollow structure plate, andthus the rigidity is decreased. Therefore, strict control of thetemperature becomes necessary in order to obtain high quality hollowstructure plates.

Furthermore, when the difference in the size (diameter ratio) betweenthe upper base and the lower base of each pin is small, not only doesthe mold-release property deteriorate, but also the following problemoccurs: in the molded hollow structure plate, the amount of resin forthe hollow protrusions is increased and the balance with the linerportion in which no hollow protrusion is formed collapses, so thatwebbing occurs and thus the formativeness deteriorates.

Furthermore, the bending elasticity gradient of the hollow structureplate is improved as the interval between the pins is smaller, butsimply reducing the interval between the pins causes webbing in thehollow structure plate more easily, especially when the difference inthe size between the upper base and the lower base of the pin is small.

Furthermore, such a hollow structure plate has a poor sound absorbency,and it is necessary to attach a porous sheet-shaped member such as anurethane foam sheet, a non-woven fabric, and a woven fabric in order toimprove the sound absorbency. Furthermore, in a commonly used soundabsorbing material, the sound absorbency depends greatly on thethickness thereof, so that for example, as the thickness of the poroussheet-shaped member becomes smaller, the sound absorbency, especially inthe low or medium frequency region, becomes poorer. Moreover, rock wool,plaster boards and the like that are used as interior materials forhouses such as ceiling materials or wall materials are lightweight andhave excellent sound absorbency and thermal insulation performance, butthe rigidity and water resistance are poor.

The present invention solves the above-described technical problems, andan object thereof is to provide a method and an apparatus formanufacturing a hollow structure plate that allow hollow protrusionprocessing and melt joining of two thermoplastic resin sheets that havebeen extrusion-molded to be performed reliably in a short time, and thatfacilitate the temperature control.

Furthermore, the present invention solves the above-described technicalproblems, and an object thereof is to provide a technique that allowshollow protrusion processing and melt joining of two thermoplastic resinsheets that have been extrusion-molded to be performed reliably in ashort time and facilitates the temperature control, and that alsoenables manufacturing of a hollow structure plate having good flexuralproperties.

Furthermore, the present invention has an object of providing alightweight hollow structure plate having excellent strength, rigidity,heat resistance, and water resistance and high sound absorbency with anappropriate thickness without attaching a porous sheet-shaped membersuch as an urethane foam, a non-woven fabric, and a woven fabric.Furthermore, the present invention has an object of providing a hollowstructure plate having high sound absorbency throughout the audiblerange by combining the above-described hollow structure plate andanother sound absorbing material, without canceling out the effect ofone another.

SUMMARY OF THE INVENTION

(1) A hollow structure plate according to the present invention is ahollow structure plate formed by fusing a plurality of hollowprotrusions that are projected in each of two thermoplastic resin sheetswith the hollow protrusions facing against one another. The hollowprotrusions are truncated cone-shaped. A ratio of a total area of alower base of each of the hollow protrusions to an area of acircumferential surface, i.e., a ratio between the total area of thelower base (opening) portions of the hollow protrusions and the area ofthe liner portions in which the hollow protrusions are not formed, is ina range from 0.3 to 0.9. A rising angle of a side face of each of thehollow protrusions in a vertical plane including a central axis of thehollow protrusion is in a range from 50 degrees to 70 degrees.

(2) A method for manufacturing a hollow structure plate according to thepresent invention comprises: introducing two thermoplastic resin sheetsinto a pressure-reduced chamber; attracting and attaching the resinsheets respectively to a circumferential surface of each of a pair ofupper and lower emboss rollers that are arranged rotatably in thepressure-reduced chamber to form a multitude of hollow protrusions oneach of the resin sheets in accordance with a shape of a pin projectedin each of the emboss rollers; and thermally fusing the end faces of thehollow protrusions in a position of a contact line, i.e., a contactpoint, of the emboss rollers. Introduction guides are arrangedrespectively above and below a sheet-introducing opening portion of thepressure-reduced chamber, each of the introduction guides being inclinedtoward a direction of the contact line, i.e., the contact point, of eachof the emboss rollers. Heating means for thermal fusion is providedbetween the introduction guides, the heating means being arranged in anon-contact manner between the resin sheets. Each of the resin sheets isattracted and attached respectively to the circumferential surface ofeach of the emboss rollers under a reduced pressure by maintainingopposing surfaces of the resin sheets in the pressure-reduced chamber atan atmospheric pressure and reducing a pressure at surfaces oppositetherefrom.

In the present invention, it is possible to provide means for insertingand guiding laterally-opposite side portions of each of the resin sheetsalong opposite side portions of the emboss rollers, and/or to laminate asurface material on an upper and a lower surface of the hollow structureplate subsequently after the hollow structure plate is molded.

Another method for manufacturing a hollow structure plate according tothe present invention comprises: introducing two thermoplastic resinsheets into a pressure-reduced chamber; attracting and attaching theresin sheets respectively to a circumferential surface of each of a pairof upper and lower emboss rollers that are arranged rotatably in thepressure-reduced chamber to form a multitude of hollow protrusions oneach of the resin sheets in accordance with a shape of a pin projectedin each of the emboss rollers; and thermally fusing the end faces of thehollow protrusions in a position of a contact line, i.e., a contactpoint, of the emboss rollers continuously. Emboss rollers satisfying thefollowing conditions are used: the pin is truncated cone-shaped; a ratioof a total area of a lower base of the pin to an area of thecircumferential surface of the emboss roller, i.e., a ratio between thetotal area of the lower base (opening) portions of the hollowprotrusions and the area of the liner portions in which the hollowprotrusions are not formed, is in a range from 0.3 to 0.9; and a risingangle of a side face of the pin in a vertical plane including a centralaxis of the pin is in a range from 50 degrees to 70 degrees.

(3) An apparatus for manufacturing a hollow structure plate according tothe present invention comprises: a pressure-reduced chamber that isevacuated to reduce a pressure inside; a pair of upper and lower embossrollers that are supported with bearings rotatably in thepressure-reduced chamber in a state in which circumferential surfaces ofthe rollers face a front opening portion of the pressure-reducedchamber, a pin provided on one of the rollers being brought into contactwith a pin provided on the other via a resin sheet in a position of acontact line, i.e., a contact point; sheet-introduction plates that arearranged respectively above and below the front opening portion, each ofthe sheet-introduction plates being inclined toward a direction of thecontact line, i.e., the contact point, of each of the emboss rollers; aplurality of border rollers that are supported rotatably on an innerside of opposite side portions of the pressure-reduced chamber; a pairof border-roller receiving and quasi-sealing members that are opposedrespectively to the border rollers with a small gap therebetween andthat are arranged on both sides of each of the emboss rollers toquasi-seal both sides of the emboss roller in the pressure-reducedchamber; rear plates that are continuous toward a rear opening portionof the pressure-reduced chamber, each of the rear plates being arrangedhorizontally toward a direction of the contact line, i.e. the contactpoint, of each of the emboss rollers on the rear side thereof; and aheater for heating that is arranged between the introduction plates.Herein, the degree of the quasi-sealing includes a degree very close tocomplete sealing, and it is preferable that the degree of the reducedpressure in the pressure-reduced chamber 10, which will be describedlater, is about 300 to 2000 mm H₂O.

Another apparatus for manufacturing a hollow structure plate accordingto the present invention comprises: a pressure-reduced chamber that isevacuated to reduce a pressure inside; a pair of upper and lower embossrollers that are supported with bearings rotatably in thepressure-reduced chamber in a state in which circumferential surfaces ofthe rollers face a front opening portion of the pressure-reducedchamber, a pin provided on one of the rollers being brought into contactwith a pin provided on the other via two thermoplastic resin sheets in aposition of a contact line, i.e., a contact point; and a heater forheating that is arranged at the front opening portion. The pin of eachof the emboss rollers is truncated cone-shaped. A ratio of a total areaof a lower base of the pin to an area of the circumferential surface ofthe emboss roller, i.e., a ratio between the total area of the lowerbase (opening) portions of the hollow protrusions and the area of theliner portions in which the hollow protrusions are not formed, is in arange from 0.3 to 0.9. A rising angle of a side face of the pin in avertical plane including a central axis of the pin is in a range from 50degrees to 70 degrees.

(4) A sound absorbing structure plate according to the present inventioncomprises a multilayer hollow structure plate constituted by attachingnon-air-permeable sheets onto front and back sides of a core memberobtained by fusing a plurality of hollow protrusions that are projectedin each of two thermoplastic resin sheets with the hollow protrusionsfacing against one another. A small hole opened between the hollowprotrusions, i.e., in the liner portions in which the hollow protrusionsare not formed (which appear like recesses after the sheet is formed),on at least one of the front and back sides of the multilayer hollowstructure plate is formed.

In the sound absorbing structure plate according to the presentinvention, it is possible to attach a sound absorbing material, forexample, a porous sheet such as an urethane foam sheet, a non-wovenfabric, and a woven fabric, onto the side on which the small hole isformed in the hollow structure plate, and/or to provide the hollowstructure plate with a Metsuke (weight per unit area) of from 700 to3000 g/m².

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram showing a hollow structure plate of thepresent invention.

FIGS. 2( a) to 2(d) show preferable embodiments of a sound absorbingstructure plate of the present invention. FIG. 2( a) is across-sectional view showing the state in the middle of manufacturing;FIG. 2( b) is a cross-sectional view showing a hollow structure platethat is an intermediate product; FIG. 2( c) is a plan view of FIG. 2(b); and FIG. 2( d) is a cross-sectional view of a sound absorbingstructure plate that is a final product.

FIG. 3 is a correlation diagram of the frequency and the reverberantabsorption coefficient in Examples 1 to 5.

FIG. 4 is a correlation diagram of the frequency and the reverberantabsorption coefficient in Examples 6 and 7.

FIG. 5 is a correlation diagram of the frequency and the reverberantabsorption coefficient in Comparative Examples 1 and 2.

FIG. 6 is a correlation diagram of the frequency and the reverberantabsorption coefficient in Example 6 and Comparative Example 2.

FIG. 7 is an explanatory diagram showing the entire structure of anapparatus to which the present invention is applied.

FIG. 8 is a side-cross-sectional explanatory diagram of themanufacturing apparatus.

FIG. 9 is a cross-sectional explanatory diagram taken along line A-A ofthe drawings.

FIG. 10 is a cross-sectional explanatory diagram taken along line B-B ofthe drawings.

FIG. 11 is an enlarged view of a portion C of the drawings.

FIG. 12 is a perspective view of an emboss roller.

FIG. 13 is an enlarged explanatory diagram of a part of the embossroller of FIG. 6.

FIG. 14 is an enlarged cross-sectional view of a step provided in a pinof the emboss roller.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference of the accompanying drawings in detail.

As shown in FIG. 1, the hollow structure plate of the present inventionis formed by fusing a plurality of hollow protrusions (referred to as“pins” or “emboss pins” in the examples) 112, 112 that are projected(embossed) in two thermoplastic resin sheets 110, 110A with the endfaces attached to each other, and characterized by the following: thepins 112, 112 are truncated cone-shaped; the ratio of the total area ofthe lower bases of the pins 112, 112 to the circumferential surface isin the range from 0.3 to 0.9; and the rising angle of the side face ofeach pin 112, 112 in the vertical plane including the central axis ofthe pin 112, 112 is in the range from 50 degrees to 70 degrees. Such ahollow structure plate also can be constituted by attachingnon-air-permeable sheets (not shown) made of thermoplastic resin sheetsto liner portions (i.e., portions between the pins 112, 112 in thethermoplastic resin sheets 110, 110 a) 114, 114 on both the front andback sides thereof.

As the resin sheet 3 used in the present invention, polyolefin resinsheets, in particular, polypropylene sheets are preferable, but otherthermoplastic resin materials in general can be applied, and setting ofa relevant part of the apparatus can be changed, depending on varioustemperature characteristics such as the melting point, the softeningpoint, and the glass transition temperature, or the properties of thematerial.

EXAMPLE 1 OF THE HOLLOW STRUCTURE PLATE

A homopropylene sheet (melting point: 165° C., softening point: 120° C.)having a thickness of 0.5 mm and a Metsuke (weight per unit area) of 500g/m² in the melted state was placed on a vacuum molding plate having awidth of 70 mm and a length of 200 mm in which pins 11 b, whose heightis 5 mm and whose diameter of the upper base 11 d is 2 mm and diameterof the lower base 11 e is 8 mm, were arranged in a staggered latticearrangement with a pin interval (interval between the rising portions 11g) of 2 mm, and vacuum molding was performed in off-line. The obtainedtwo embossed sheets were attached in such a manner that the pins thereofwere attached with an ultrasonic fusing apparatus. Using this as a coremember, homopropylene sheets having a thickness of 0.25 mm and a Metsukeof 250 g/m² were attached as face material to the front and the back ofthis core member. Thus, a hollow structure plate having a thickness of10.5 mm and a Metsuke of 1500 g/m² was obtained. Thereafter, a bendingtest was performed according to JIS K 7203. Regarding the bendingelasticity gradient, a load when a flexure of 1 cm occurred was obtainedbased on the straight portion of a load-flexure curve obtained by theabove-described bending measurement, and this was taken as the bendingelasticity gradient.

EXAMPLE 2 OF THE HOLLOW STRUCTURE PLATE

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 2 mm and diameter of the lower base 11 e is 6 mm,were arranged in a staggered lattice arrangement with a pin interval of2 mm. Thereafter, a bending test was performed.

EXAMPLE 3 OF THE HOLLOW STRUCTURE PLATE

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 2 mm and diameter of the lower base 11 e is 6 mm,were arranged in a staggered lattice arrangement with a pin interval of4 mm. Thereafter, a bending test was performed.

EXAMPLE 4 OF THE HOLLOW STRUCTURE PLATE

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 4 mm and diameter of the lower base 11 e is 8 mm,were arranged in a staggered lattice arrangement with a pin interval of2 mm. Thereafter, a bending test was performed.

EXAMPLE 5 OF THE HOLLOW STRUCTURE PLATE

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 2 mm and diameter of the lower base 11 e is 10 mm,were arranged in a staggered lattice arrangement with a pin interval of2 mm. Thereafter, a bending test was performed.

EXAMPLE 6 OF THE HOLLOW STRUCTURE PLATE

The pin was configured to have a step. A hollow structure plate wasobtained in the same manner as Example 1, using a vacuum molding platehaving a width of 70 mm and a length of 200 mm in which pins 11 b, whoseheight is 5 mm and whose diameters of the upper base 11 d, the innerside of the intermediate state, the outer side of the intermediatestage, and the lower base 11 e are 1.5 mm, 3 mm, 5 mm, and 6 mm,respectively, were arranged in a staggered lattice arrangement with apin interval of 2 mm. Thereafter, a bending test was performed.

Comparative Example 1 of the Hollow Structure Plate

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 4 mm and diameter of the lower base 11 e is 6 mm,were arranged in a staggered lattice arrangement with a pin interval of4 mm. Thereafter, a bending test was performed.

Comparative Example 2 of the Hollow Structure Plate

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 2 mm and diameter of the lower base 11 e is 4 mm,were arranged in a staggered lattice arrangement with a pin interval of4 mm. Thereafter, a bending test was performed.

Comparative Example 3 of the Hollow Structure Plate

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 6 mm and diameter of the lower base 11 e is 8 mm,were arranged in a staggered lattice arrangement with a pin interval of4 mm. Thereafter, a bending test was performed.

Comparative Example 4 of the Hollow Structure Plate

Molding was performed in the same manner as Example 1, using a vacuummolding plate having a width of 70 mm and a length of 200 mm in whichpins 11 b, whose height is 5 mm and whose diameter of the upper base 11d is 4 mm and diameter of the lower base 11 e is 6 mm, were arranged ina staggered lattice arrangement with a pin interval of 2 mm. Webbingoccurred, and a satisfactory hollow structure plate was not obtained.

Comparative Example 5 of the Hollow Structure Plate

A hollow structure plate was obtained in the same manner as Example 1,using a vacuum molding plate having a width of 70 mm and a length of 200mm in which pins 11 b, whose height is 5 mm and whose diameter of theupper base 11 d is 2 mm and diameter of the lower base 11 e is 12 mm,were arranged in a staggered lattice arrangement with a pin interval of2 mm. Thereafter, a bending test was performed.

Test Results

Table 1 shows the results of the bending tests of the above examples andcomparative examples.

TABLE 1 pin diameter ratio of pin bending (φ) pin total area of risingelasticity (upper base– interval pin lower angle gradient lower base)(mm) base*1 (°) (N/cm) Ex. 1 2-8 2 0.58 61 530 Ex. 2 2-6 2 0.51 68 500Ex. 3 2-6 4 0.33 68 420 Ex. 4 4-8 2 0.58 68 430 Ex. 5  2-10 2 0.63 51410 Ex. 6*2 1.5-(3-5)-6 2 0.51 — 530 Com. Ex. 1 4-6 4 0.33 79 310 Com.Ex. 2 2-4 4 0.23 79 340 Com. Ex. 3 6-8 4 0.40 79 325 Com. Ex. 4 4-6 20.51 79 webbing Com. Ex. 5  2-12 2 0.74 45 280 *1: when taking the totalarea of an embossed sheet (one face) as 1. *2: a pin having a step

The above results make it clear that the above-described Examples havethe effect of the present invention, as evident in contrast to theComparative Examples.

The present invention not only allows hollow protrusion processing andmelt joining of two thermoplastic resin sheets that have beenextrusion-molded to be performed reliably in a short time andfacilitates the temperature control, but also enables a hollow structureplate having good bending characteristics to be manufactured.

FIGS. 2( a) to 2(d) show preferable embodiments in which the hollowstructure plate is used as a sound absorbing structure plate of thepresent invention. The sound absorbing structure plate shown in thesefigures is provided with a hollow structure plate 140 and a soundabsorbing material 150. The hollow structure plate 140 is constituted byattaching non-air-permeable sheets 130, 130A made of thermoplastic resinsheets to liner portions (i.e., portions between the hollow protrusions112, 112 in the thermoplastic resin sheets 110, 110 a) 114, 114 of thecore member 120 on both the front and back sides thereof. The coremember 120 is formed by fusing a plurality of hollow protrusions (alsoreferred to as “pins” or “emboss pins”) 112, 112 that are projected(embossed) in two thermoplastic resin sheets 110 and 110A with their endfaces attached facing each other. The sound absorbing material 150 ismade of porous material that is attached to at least one of the twofaces of the front and the back of the hollow structure plate 140. Smallholes 114 a, 130 a that are opened toward the closed spaces 142, 142 inthe hollow structure plate 140 are formed in the liner portions 114 ofthe thermoplastic resin sheet 110 that is positioned on the side towhich the sound absorbing material 150 is attached, and in the non-airpermeable sheet 130 only at the positions that match the liner portions114.

According to this embodiment, noise in a relatively high frequency bandcan be absorbed with the sound absorbing material 150, and noise in arelatively low frequency band can be absorbed by achieving a resonantabsorbing effect of the hollow portions (air layers) of the hollowstructure plate 140 that are opened through the small holes 130 a and114 a. Thus, a sound absorbing structure plate having high absorbencythroughout the audible range, without canceling out the effect of oneanother, can be obtained.

In addition, since the thermoplastic resin sheets 110, 110A are mainmembers, the sound absorbing structure plate is lightweight, andfurther, since the hollow protrusions 112, 112 are fused with their endfaces attached facing each other, the sound absorbing structure platehas high strength and high rigidity.

There is no limitation regarding the thermoplastic resin that is the rawmaterial for the core member 120. However, in view of the balancebetween the cost, the formability, the properties, and othercharacteristics, polypropylene is preferable. There is no limitationregarding the raw material of the non-air-permeable sheets that areattached to both faces of the core member. However, in view of thebalance between the cost, the formability, the properties, and othercharacteristics, polypropylene is preferable. Moreover, fillers such asmica and talc or modifiers such as a flame retardant for providing flameresistance can be added to these raw materials. The sound structureplate can be provided with excellent recycling properties by usingpolypropylene.

It is preferable that the Metsuke (weight per unit area) of the hollowstructure plate 140 is approximately from 700 to 3000 g/m². When theMetsuke is too small, the thickness of the hollow protrusions 112, 112is too small and they are made into films, and therefore sufficientstrength and rigidity cannot be obtained. On the other hand, when theMetsuke is too large, the advantage of light weight may be impaired. Thethickness is preferably, for example, approximately from 6 to 15 mm,depending on the application. The hollow protrusions 112, 112 of thethermoplastic resin sheets 110, 110 a constituting the hollow structureplate 140 are hollow conical in the figures, but may be hollowcylindrical.

As shown in FIG. 2( c), the small holes 114 a, 130 a are not necessarilyprovided in every interval between the hollow protrusions 112, and canbe provided at an appropriate pitch. It is preferable that the holediameter is from φ0.3 to 7.0 mm. When the diameter is smaller than 0.3mm, processing is difficult, and when it exceeds 7.0 mm, not only isprocessing difficult, but the rigidity also deteriorates, because theleg portion of the hollow protrusion 112 is destroyed at the time ofopening holes. More preferably, it is from φ0.5 to 4.0 mm. Furthermore,there is no limitation regarding the number and the total area of thesmall holes. The hole diameter can be selected as appropriate within theabove-described range, and can be adjusted in accordance with a specificfrequency that is desired to be absorbed, depending on the application.The small holes can be formed by a method having processing propertiesthat can be selected as appropriate, such as drilling, needling, andpunching.

In FIG. 2, the small holes 114 a, 130 a are formed only in the linerportions 114 of the thermoplastic resin sheet 110 positioned on the side(the upper side in FIG. 2) to which the sound absorbing material isattached and the non-air permeable sheet 130 that matches therewith, butthey may be formed in the end faces and circumferential faces of thehollow protrusions 112 of the thermoplastic resin sheet 110. Moreover,the small holes 114 a, 130 a may also be formed in the liner portions114 of the thermoplastic resin sheet 110A positioned on the side towhich the sound absorbing material is not attached (the lower side inFIG. 2) and the non-air permeable sheet 130A that matches therewith. Inthis case, the positions of the small holes 114 a, 130 a may be matchedbetween both the front and back sides of the hollow structure plate 140,or do not have to be matched. The hole diameter and/or the pitch of allthe small holes 114 a, 130 a in the present invention do not necessarilyhave to be equal, and the small holes may be arranged either regularlyor irregularly.

In this embodiment, a multilayered hollow structure plate is configuredby attaching the sound absorbing material 150 only on one face (the sideon which the small hole 114 a is formed in the liner portions 114 of thethermoplastic resin sheet 110) of the hollow structure plate 140.However, the sound absorbing material 150 may also be attached to theother face of the hollow structure plate 140. The sound absorbingmaterial 150 is, for example, a foam member such as a sponge memberhaving continuous air bubbles, and attaching a porous material such as anon-woven fabric can further enhance the sound absorbing effect.

Example 1

A homopolypropylene sheet (melting point: 165° C., softening point: 120°C.) having a thickness of 0.5 mm and a Metsuke (weight per unit area) of500 g/m² in the melted state was placed on a vacuum molding plate havinga length of 1000 mm and a width of 1000 mm in which hollow protrusions(emboss pins), whose height is 5.5 mm and whose diameter of the upperbase is 2 mm and diameter of the lower base is 6 mm, were arranged in astaggered lattice arrangement with a pin interval of 2 mm, and vacuummolding was performed in off-line. The ends of the protrusions of theobtained two embossed sheets were thermally fused. Using this as a coremember, homopolypropylene sheets having a thickness of 0.25 mm and aMetsuke of 250 g/m² were attached as face material to the front and theback of this core member. Thus, a hollow structure plate having a totalthickness of 11.5 mm and a Metsuke of 1500 g/m² was obtained.Thereafter, a hole-opening process was performed to one of the linerportions of the hollow structure plate such that holes of φ1.0 wereformed at an equal pitch at an opening ratio of 0.36%. The soundabsorption coefficient of this perforated hollow structure plate of 1×1m was measured in a small reverberant chamber (manufactured by NittoboAcoustic Engineering Co., Ltd.).

Example 2

A hollow structure plate was obtained in the sane manner as in Example1, and then a hole-opening process was performed to one of the linerportions of the hollow structure plate such that holes of φ2.5 mm wereformed at an equal pitch at an opening ratio of 0.36%. The soundabsorption coefficient of this perforated hollow structure plate wasmeasured in a small reverberant chamber.

Example 3

A hollow structure plate was obtained in the same manner as in Example1, and then a hole-opening process was performed to one of the linerportions of the hollow structure plate such that holes of φ4.0 mm wereformed at an equal pitch at an opening ratio of 0.36%. The soundabsorption coefficient of this perforated hollow structure plate wasmeasured in a small reverberant chamber.

Example 4

A hollow structure plate was obtained in the same manner as in Example1, and then a hole-opening process was performed to one of the linerportions of the hollow structure plate such that holes of φ2.5 mm wereformed at an equal pitch at an opening ratio of 0.19%. The soundabsorption coefficient of this perforated hollow structure plate wasmeasured in a small reverberant chamber.

Example 5

A hollow structure plate was obtained in the same manner as in Example1, and then a hole-opening process was performed to one of the linerportions of the hollow structure plate such that holes of φ2.5 mm wereformed at an equal pitch at an opening ratio of 0.66%. The soundabsorption coefficient of this perforated hollow structure plate wasmeasured in a small reverberant chamber.

Example 6

A hollow structure plate was obtained in the same manner as in Example1, and then a soft urethane foam having a thickness of 6 mm was attachedas a sound absorbing material to the face having the holes of thishollow structure plate, so that a multilayered hollow structure platewas produced. Then, the sound absorption coefficient was measured in asmall reverberant chamber (t=1 means a thickness of 1 mm).

Example 7

A hollow structure plate having holes was obtained in the same manner asin Example 2, and then an air-permeable surface material having athickness of 6 mm and a soft urethane foam (t=5) were attached as soundabsorbing materials to the face having the holes of this hollowstructure plate, so that a multilayered hollow structure plate wasproduced. Then, the sound absorption coefficient was measured in a smallreverberant chamber.

Comparative Example 1

A hollow structure plate was produced in the same manner as in Example1, and the sound absorption coefficient was measured in a smallreverberant chamber.

Comparative Example 2

The sound absorption coefficient of a soft urethane foam having athickness of 6 mm was measured in a small reverberant chamber.

Comparative Example 3

A hollow structure plate was obtained in the same manner as in Example1, and a multilayered hollow structure plate was produced by attaching asound absorbing material made of a foam material under the sameconditions as in Example 6, except that no holes were opened. Then, thesound absorption coefficient was measured according to the reverberantchamber method. The sound absorption coefficient in certain frequenciesof Comparative Example 3 is shown in Table 2.

Table 2 show the results of measuring the reverberant sound absorptioncoefficient of Examples 1 to 7 and Comparative Examples 1 to 3, andTable 3 shows the bending elasticity gradient.

TABLE 2 Results of measuring the reverberant sound absorptioncoefficient Com. Com. Com. frequency (Hz) Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5Ex. 6 Ex. 7 Ex. 1 Ex. 2 Ex. 3 200 −0.03 −0.03 0.10 −0.05 0.08 0.16 0.020.00 0.05 0.05 250 0.04 0.06 0.25 0.14 0.16 0.18 0.14 0.20 0.08 0.07 315−0.07 −0.09 −0.06 −0.04 −0.08 0.01 −0.01 0.06 −0.06 −0.03 400 −0.02 0.030.08 0.06 0.02 0.17 0.21 0.12 0.01 0.00 500 0.04 0.06 0.05 0.11 0.050.25 0.31 0.12 0.02 0.02 630 0.14 0.20 0.26 0.42 0.10 0.51 0.51 0.150.10 0.09 800 0.28 0.42 0.50 0.49 0.25 0.53 0.55 0.10 0.09 0.10 10000.49 0.50 0.42 0.35 0.46 0.62 0.46 0.07 0.14 0.15 1250 0.63 0.46 0.280.21 0.63 0.63 0.45 0.10 0.19 0.19 1600 0.56 0.31 0.17 0.13 0.54 0.540.41 0.06 0.34 0.33 2000 0.45 0.26 0.19 0.16 0.50 0.52 0.52 0.13 0.520.52 2500 0.29 0.16 0.16 0.10 0.28 0.57 0.57 0.11 0.52 0.50 3150 0.200.10 0.11 0.08 0.12 0.55 0.60 0.08 0.57 0.58 4000 0.11 0.10 0.09 0.050.14 0.69 0.66 0.09 0.69 0.70 5000 0.10 0.08 0.12 0.08 0.11 0.78 0.780.12 0.75 0.74

TABLE 3 bending hole opening elasticity diameter ratio gradient (mmφ)(%) (N/cm) note Ex. 1 1.0 0.36 600 Ex. 2 2.5 0.36 600 Ex. 3 4.0 0.36 580Ex. 4 2.5 0.19 620 Ex. 5 2.5 0.66 590 Ex. 6 1.0 0.36 610 Ex. 7 2.5 0.36600 Com. Ex. 1 — 0 600 Ex. 1, no hole Com. Ex. 2 — 0 330 Ex. 2, PP sheetattached to one face, no hole + foam material Com. Ex. EX — 0 610 Com.Ex. 1 + foam material

FIGS. 3 to 6 are correlation diagrams of the frequency and reverberantsound absorption coefficient in Examples 1 to 7 and Comparative Examples1 to 3. Tables 2 and 3 and FIGS. 3 to 6 indicate the following.

In Examples 1 to 5, it was confirmed that noise in a relatively lowfrequency band can be absorbed. Furthermore, it was proved that thenatural frequency can be changed by changing the size of the smallholes, the opening ratio, etc., and thus that the degree of freedom indesigning for use as a sound absorbing material is large.

For porous materials such as foam materials having continuous airbubbles and non-woven fabrics, the larger the thickness is, the higherthe sound absorption performance becomes When there is a limitation ofthe thickness, the sound absorption performance, especially in the lowor medium frequency range, deteriorates. Therefore, as in Examples 6 and7, a multilayered hollow structure plate is produced by attaching arelatively thin porous sheet as a sound absorbing material to the facehaving holes of the hollow structure plate so that the merits of the twomembers are reinforced by each other. Thus, it has been proven that inthis way, the sound absorption performance is enhanced over a wide rangeof frequency bands.

Furthermore, it was also confirmed that the sound absorption coefficientof the multilayered hollow structure plate shown as Comparative Example3, which was produced by attaching a surface material and a foammaterial without opening a hole in the hollow structure plate, wassubstantially equal to that of the soft urethane foam material ofComparative Example 2.

Furthermore, Table 3 indicates that the bending elasticity gradient ofthe sound absorbing plate of the present Examples is large and exhibitsrelatively high rigidity.

As evident from the above description, according to the sound absorbingstructure plate of the present invention, the sound absorbency can beprovided with a small increase in the weight and without reducing therigidity. Furthermore, the sound absorbing characteristics for anyfrequency band can be provided by combining another sound absorbingmaterial. Moreover, the sound absorbing structure plate can be recycledeasily by selecting the material. As a result, the sound absorbingstructure plate can be used preferably as a sound absorbing interiormaterial of building or vehicles.

The hollow structure plate or the sound absorbing structure plate of thepresent invention described above can be produced preferably with amanufacturing apparatus described below by a manufacturing methoddescribed below.

FIG. 7 shows the entire configuration of an apparatus to which themethod of the present invention is applied. In FIG. 7, T-dies 2 areprovided at each end of a pair of extruders 1 that are arranged inparallel. As regards the thermoplastic resin sheets 3 extruded from theT-dies 2, protrusions of the resin sheets 3 are molded and the sheetsare attached using a molding apparatus or a manufacturing apparatus ofthe present invention (hereinafter, referred to as a “manufacturingapparatus”, but both mean the same) 4 that performs both molding ofprotrusions and attachment. Thereafter, surface materials 6 arelaminated on the upper and the lower surfaces thereof with a laminatingapparatus 5, and the laminated sheets are taken up by a take-up device 7at a predetermined speed. Then, the sheets are sequentially cut by acutting device, which is not shown, so as to be completed as a product.

Among the above, the manufacturing apparatus 4 that is the main part ofthe present invention is provided with, as shown in FIGS. 8 to 10, apair of pressure-reduced chambers 10 that are formed half-divided intothe upper and the lower portions; emboss rollers 11 that are supportedwith bearings in the pressure-reduced chambers 10 and whosecircumferential surfaces face the side of opening portions 10 a that areopened in the juncture position of the pressure-reduced chambers 10;sheet-introduction plates 12 that are arranged in the upper and thelower inner sides of the opening portions 10 a and are inclined towardthe direction of the contact line, i.e., a contact point, on thecircumferential surface of the emboss roller 11 (hereinafter, referredto as “contact point”); a plurality of border rollers 15 that aresupported rotatably inside the opposite sides of the pressure-reducedchambers 10; a pair of border-roller-receiving and quasi-sealing members14 that are opposed to the border rollers 15 with a small gap and arearranged on both the sides of each emboss roller 11 to quasi-seal boththe sides of each emboss roller 15 in the pressure-reduced chambers 10;rear plates 16 that are arranged horizontally toward the contact pointdirection in the back of the emboss rollers 12 and are continuous towardthe rear opening portion 10 b of each pressure-reduced chamber 10; and aheater for heating 17 having a triangular cross section that is providedbetween the introduction plates 12.

Suction ports 10 c for reducing pressure are opened on the upper and thelower portions of each of the pressure-reduced chambers 10. Thepressure-reducing suction ports 10 c are connected to a vacuum pump,which is not shown, via a hose, which is also not shown, and thepressure-reduced chambers 10 are evacuated to reduce the pressure, sothat an atmospheric pressure is present between the two resin sheets 3that are supplied toward the opening portion 10 a, and the faces on theside of the emboss rollers 11 are in a reduced pressure, so that thedifference in the pressure allows the two resin sheets 3 to be attractedto the surfaces of the two emboss rollers 11 and attached to thesurfaces.

In the two emboss rollers 11, as shown in FIG. 11, a multitude of pins11 b are projected in a vertically and horizontally regular manner onthe surface of the rollers 11 a made of metal such as steel or aluminumdie-cast. The shaft portions 11 c of the rollers 11 a are in the outerside faces of the two pressure-reduced chambers 10, and are operated incooperation with a gear or a timing pulley so as to be rotated in theopposite directions from each other toward the conveying direction ofthe resin sheets 3. One of the shaft portions 11 c is driven to berotated by a motor, which is not shown. This motor drives each embossroller 11 to rotate at a speed that is in synchronization with thetake-up speed of the take-up device 7.

Furthermore, in the emboss rollers 11, holes (not shown) having adiameter, for example, of about 2 mm (preferably from 1 to 5 mm) areformed in the trough portion (flat portions other than the pins 11 b) ofthe rollers 11 a in order to prevent air accumulation from occurringbetween the resin sheets 3 and the emboss rollers 11. These holes are incommunication with the inside of the pressure-reduced chambers 10. Thus,there is no difference in the degree of the reduced pressure between theinside of the pressure-reduced chambers 10 and the inside of the embossrollers 11, so that the resin sheets 3 can be attracted to the embossrollers 11 uniformly. Therefore, the emboss rollers 11 allow theinternal portions to be hollow. The holes can be provided at such aratio that one hole is formed for every 1.5 to 2 pins 11 b; for example,holes can be provided in every trough portion formed with the pins 11 b,or can be provided in such a ratio that one hole is formed for aplurality of trough portions.

Furthermore, the pins 11 b are brought in contact in a line via theresin sheets 3 at the contact point of the upper and the lower embossrollers 11, making thermal fusion possible by pressing to attach theresin sheets 3 with each other at this position.

The introduction plates 12 function to minimize the gap between theopening portion 10 a and the resin sheets 6 that are introducedtherefrom and to maintain a reduced pressure inside the pressure-reducedchambers 10.

The border-roller-receiving and quasi-sealing members 14 function toconvey the resin sheets 3 to the rear by the rotation thereof whileholding the laterally-opposite side portions of the resin sheets 3 incooperation with the border rollers 15 and maintaining the state inwhich the resin sheets 3 are pressed onto the emboss rollers 11.

The heater 17 for heating serves to heat the opposing surfaces of thetwo resin sheets 3 to a temperature higher than the temperature at whichthey are melted and extruded to increase the temperature so as to ensurethermal fusion with the emboss rollers 11.

In the above, the resin sheets 3 in a semi-melted state that areextruded from the T-dies 2 are brought in contact with the upper and thelower emboss rollers 11 and are attracted and attached thereto while thepressure is evacuated and reduced from the upper and the lower surfacesin the manufacturing apparatus 4. As a result, a multitude of hollowprotrusions 3 a are formed in accordance with the shape of the pins 11b. Then, at the contact point of the emboss rollers 11, the respectivepins 11 a are brought in contact via the resin sheets 3, so that the endfaces of the hollow protrusions 3 a are thermally fused bythermo-compression by this contact. In other words, in this position,the contact surfaces of the two resin sheets 3 are cooled and solidifiedbecause the heat of the contact surfaces is deprived of by the embossrollers 11. On the other hand, the surfaces opposite thereto are heatedby the heater for heating 17 and are melted. Thus, thermal fusion can beperformed easily.

After fusion, the sheets are easily released from the pins 11 b for thesame reason, and are let out from the rear opening portion 10 b of thepressure-reduced chambers while being guided by the rear plates 16 andfurther cooled.

For the resin sheets 3 used for the above molding, polyolefin resinsheets, in particular, polypropylene sheets are preferable, but otherthermoplastic resin materials in general can be used simply by changingthe setting of a relevant part of the apparatus, depending on thevarious temperature characteristics such as the melting point, thesoftening point, the glass transition temperature or the properties ofthe material.

For example, when homopolypropylene (melting point: 165° C., softeningpoint: 120° C.) is selected as an extrusion molding material, thesurface temperature after extrusion is preferably a setting temperatureof approximately from 150 to 200° C. in the vicinity of the frontopening portion 10 a. When the temperature is lower than this settingtemperature, the material is difficult to deform so that molding under areduced pressure cannot be performed. On the other hand, if thetemperature is higher than the upper limit of the setting temperature,then the material is softened so that the shape-retaining properties ofthe resin sheets 3 deteriorate at the time of supply. Therefore, thetemperature is set to be in the above-described range.

It is preferable that the heater temperature is from 280° C. to 320° C.,and the heater 17 for heating is provided away from the two resin sheets3 by 0.1 mm to 2 mm, preferably 0.3 to 1.2 mm, so that the resin sheetscan be prevented from getting stuck to the rollers.

The degree of the reduced pressure in the pressure-reduced chambers 10is from 300 to 2000 mm H₂O, preferably from 400 to 600 mm H₂O, tofacilitate molding under a reduced pressure.

The gap between the plates 12, 16 and the emboss rollers 11 ispreferably as small as possible in order to maintain the reducedpressure, and can be set to 1 mm or less, and preferably about 0.2 mm.However, this value is set for the purpose of preventing the contact ofthe plates 12, 16 to the emboss rollers 11 and ensuring the degree ofthe reduced pressure as much as possible, and therefore the gap can bemade smaller, depending on the machine precision.

Each of the pins 11 b of the emboss rollers 11 is truncated cone-shaped,as shown in the drawings. Practical sizes are preferably as follows: thedifference in the size between the upper base and the lower base is 2mm; the pin diameter is from 5 to 10 mm; the height is from 3 to 6 mm;and the pin pitch is from 10 to 15 mm. Thus, a hollow structure that iscompleted to be molded with these sizes has a thickness of from 6 to 12mm, a weight of from 500 to 2,000 g/m², an in-plane compressive strengthof from 0.5 to 1.5 MPa, a fracture load by bending of from 30 to 100 N,and a bending elasticity gradient of from 80 to 200 N/cm. Thus, a hollowstructure having high strength for its thickness and its weight can beobtained. It should be noted that the in-plane compressive strength ismeasured according to JIS Z 0401, and the fracture load by bending ismeasured according to JIS K 7203. For the bending elasticity gradient, aload when a flexure of 1 cm occurred is obtained based on the straightportion of a load-f lexure curve obtained by the above-described bendingmeasurement, and this was taken as the bending elasticity gradient.

Next, as shown in FIG. 7, the laminating apparatus 5 includes calenderrolls 20 for transferring an adhesive sequentially to the surfacematerials 6 that are let out from stock rolls 6 a, and a pair oflaminate rollers 21 arranged in the upper and the lower portions in theconveying path of the molded hollow structure. In place of using thelaminating means employing an adhesive, thermal adhesion or otheradhering means can be selected as appropriate.

Any materials can be used as the surface material 6, as long as it canbe used for the purpose of closing the hollow protrusions 3 a. Forexample, polypropylene sheets, which are the same material, can be used,or various sheet materials for decoration can be used when the hollowstructure plate is used as, for example, an interior material forvehicles such as a ceiling material.

The above-described laminating apparatus 5 is not always necessary, anda hollow structure that is molded in the manufacturing apparatus 4 maybe taken up as it is by the take-up device 7, and be made as anintermediate product.

Here, a hollow structure was molded by selecting homopolypropylene(melting point: 165° C., softening point: 120° C.) as an extrusionmolding material, and setting the thickness of each resin sheet to 0.25mm and the surface temperature after extrusion to about 180° C. in thevicinity of the front opening portion 10 a of the pressure-reducedchambers 10. The temperature of the heater was heated to 300° C. and wasplaced 0.7 mm away from the two resin sheets 3 to prevent the resinsheets from getting stuck to the rollers. The degree of the reducedpressure of the pressure-reduced chamber 10 was 500 mm H₂O, and thetake-up speed of the take-up device was 1.0 m/sec.

A hollow structure after completion of molding had a thickness of 11.0mm, a weight of 1,000 g/m², an in-plane compressive strength of 1.0 MPa,a fracture load by bending MD of 52 N and TD of 47 N, and a bendingelasticity gradient MD of 102 N/cm and TD of 92 N/cm. Thus, a hollowstructure having high strength for its thickness and its weight wasobtained.

On the other hand, when a hollow structure was molded using the sameresin material and the same conditions but in a process in which heatingwith the heater 17 was omitted, the upper and the lower sheets were notattached or integrated, and therefore a desired hollow structure couldnot be obtained.

Thus, according to the present invention, hollow protrusion processingand melt joining of two thermoplastic resin sheets that have beenextrusion-molded can be performed reliably in a short time. Furthermore,the resin of the top portion of each hollow protrusion, produced byusing the technique of the present invention can be easily made thickerthan the leg portion, so that the top portions of the hollow protrusionscan be attached and joined stably, compared with hollow protrusionswhose top portions are made of thin resin.

In the above manufacturing apparatus, the pins 11 b of the embossrollers 11 are truncated cone-shaped (frustum of a cone), as shown inFIG. 13. The ratio of the total area of the lower bases 11 e of the pins11 b, which are provided on the circumferential surface 11 a of theemboss roller 11, to the area of the circumferential surface 11 a of theemboss roller is in the range from 0.3 to 0.9. Moreover, the risingangle θ of the pin side face 11 f in the vertical plane (sheet plane inFIG. 13) including the central axis 11 h of the pin 11 b (i.e., theangle formed with the contact point of the roller circumferentialsurface 11 a at the rising portion 11 g of the pin 11 b) is in the rangefrom 50 degrees to 70 degrees.

In other words, for example, when the height of the pin is 5 mm: thedifference in the size between the upper base 11 d and the lower base 11e is approximately from 3 to 5 mm; the ratio in diameter between theupper base and the lower base is in the range from 3:5 to 1:5, and inparticular, in the range from 1:2 to 1:4; and the angle forming aprotrusion 11 j of the pin is an obtuse angle.

There is no limitation regarding the interval between the pins, but thesmaller the interval is, the better the bending rigidity becomes. In theabove-described range of the pin angle (from 50 to 70°), the intervalbetween the pins is preferably set in the range from 0 to 4.0 mm, andmore preferably, in the range from 1.5 to 2.5 mm, in view of theproduction cost (when the interval is small, a large number of pins isnecessary), secondary processing (hole-opening processing when appliedto a sound absorbing plate) or the like.

According to the above, the mold release property of the resin sheets 3from the emboss rollers 11 is improved, and webbing does not occur evenif the pin interval is reduced. In addition, the bending characteristics(in particular, bending elasticity gradient) of the produced hollowstructure plate are improved.

Furthermore, as shown in FIG. 14, the pin 11 b can be shaped to have astep. In other words, the pin 11 b is formed so as to have a recess 11 kon the side face 11 f thereof. In this case, it is preferable that boththe protrusion 11 j and the recess 11 k, which are formed on the pinside face 11 f, have obtuse angles. By doing this, the variation in thethickness between the produced hollow protrusions and the liner portionsis reduced. Therefore, the bending elasticity gradient of the producedhollow structure plate is further improved.

It should be noted that it is also possible to provide a plurality ofsteps. Moreover, in the present invention, it is possible to configurethe pin side face in the vertical plane including the central axis ofthe pin to be curved.

1. A hollow structure plate formed by fusing a plurality of hollowprotrusions that are projected in each of two thermoplastic resin sheetswith end faces of the hollow protrusions facing against one another,wherein said hollow protrusions are truncated cone-shaped, wherein aratio between a total area of lower base portions of said hollowprotrusions and an area of liner portions of the thermoplastic resinsheets is in a range from 0.3 to 0.58, wherein the lower base portionsof said hollow protrusions are open portions of said hollow protrusionswhich are opposite to the end faces of the hollow protrusions, and theliner portions of the thermoplastic resin sheets are portions of thethermoplastic resin sheets in which the hollow protrusions are notformed, wherein a rising angle of a side face of each of said hollowprotrusions in a vertical plane including a central axis of the hollowprotrusion is in a range from 50 degrees to 70 degrees, and wherein abending elasticity gradient of said hollow structure plate is equal toor greater than 420 N/cm.
 2. A method for manufacturing a hollowstructure plate comprising: introducing, using a pair ofsheet-introduction plates, two thermoplastic resin sheets into apressure-reduced chamber; attracting and attaching the thermoplasticresin sheets respectively to a circumferential surface of each of a pairof upper and lower emboss rollers that are arranged rotatably in saidpressure-reduced chamber to form a multitude of hollow protrusions oneach of the thermoplastic resin sheets in accordance with a shape of aplurality of pins projected from each of the emboss rollers; andthermally fusing, using a heater that is disposed between the pair ofsheet-introduction plates, the end faces of said hollow protrusions in aposition of a contact point of the emboss rollers continuously; whereinthe pair of sheet-introduction plates are inclined in a direction towardthe contact point; and wherein the emboss rollers satisfy the followingconditions: each of said pins is truncated cone-shaped; a ratio betweena total area of lower base portions of the pins and a surface area ofsaid emboss rollers on which the pins are not formed, is in a range from0.3 to 0.58; and a rising angle of a side face of each of the pins in avertical plane including a central axis of the pin is in a range from 50degrees to 70 degrees.
 3. An apparatus for manufacturing a hollowstructure plate comprising: a pressure-reduced chamber that is evacuatedto reduce a pressure inside; a pair of upper and lower emboss rollersthat are supported with bearings rotatably in said pressure-reducedchamber in a state in which circumferential surfaces of the embossrollers face a front opening portion of said pressure-reduced chamber,wherein a plurality of pins provided on one of the emboss rollers isbrought into contact with a plurality of pins provided on the other ofthe rollers via two thermoplastic resin sheets in a position of acontact point; a pair of sheet-introduction plates for introducing thetwo thermoplastic resin sheets into the pressure-reduced chamber, thepair of sheet-introduction plates being inclined in a direction towardthe contact point; and a heater for heating that is arranged at saidfront opening portion of said pressure-reduced chamber between the pairof sheet-introduction plates; wherein each of said pins of said embossrollers is truncated cone-shaped; wherein a ratio between a total areaof lower base portions of the pins and a surface area of said embossrollers on which the pins are not formed, is in a range from 0.3 to0.58; and wherein a rising angle of a side face of each of the pins in avertical plane including a central axis of the pin is in a range from 50degrees to 70 degrees.